Prior art studies of the human skin have shown that epidermal tissue supports a relatively large population of microorganisms, which predominantly comprise bacteria. Skin bacteria are divided into essentially two categories: (1) transient bacteria, which come and go during the course of ordinary day-to-day contact of human skin with its environment, and (2) resident bacteria, which thrive on human skin over an indefinite period of time.
While transient bacteria are readily removed by normal washing with ordinary soap, resident bacteria are more difficult to remove because they are more deeply embedded in the skin. Resident bacteria can be classified into two types, gram-positive and gram-negative, according to their reaction to the well-known Gram staining method. It is known that when gram-positive bacteria come into contact with the axillary secretions of apocrine sweat, which are normally sterile and odorless, gram-positive bacteria cause these secretions to become malodorous, thus producing the typical acrid body odor. In contrast to gram-positive types of bacteria, gram-negative bacteria are not a cause of body odor. However, over 99% of resident bacteria are of the odor-causing gram-positive variety.
Thus, the prevention or amelioration of human body odor can be brought about by reducing the number of resident gram-positive bacteria in or on the skin. This can be accomplished by regular washings with deodorant soaps and/or the application of other deodorant preparations such as aerosol spray deodorants, sticks, creams, etc., which contain active antibacterial ingredients.
It has now been discovered that when hops, i.e., the flower of the humulus lupulus plant, is extracted with an organic solvent and the solvent is removed, a residue, or extract, is obtained which acts as an effective bacteriostatic agent in soaps and other cosmetic preparations for application to human skin and which prevents or ameliorates body odor. It has been found, for example, that soap solutions containing only relatively minor amounts, e.g., about 1% by weight, of the hop extract, effectively inhibit the growth of odor-causing skin bacteria such as Staphylococcus aureus and Staphylococcus epidermis.
The antibacterial activity of hop extract in the presence of soaps and other preparations for human skin has not been previously known. Although certain constituents of hops have been known to exert antibacterial activity against the very fastidious microorganisms that exist in beer, it is unexpected that hop constituents can act as effective antibacterial ingredients in soaps and other cosmetic compositions, which have often been found to neutralize or destroy the microbicidal or bacteriostatic power of antiseptic compounds. The hop extract of this invention possesses a number of other properties, in addition to bacteriostatic activity, which make it suitable for use in deodorant preparations. It is surprisingly compatible with other ingredients employed in deodorant preparations, substantive to human skin, i.e., sticks to human skin, soluble in soaps and oils, non-toxic to animal life and non-irritating to human skin.